1. Field of Invention
This invention relates to scanning devices and methods.
2. Description of Related Art
In a carriage-type ink jet printer, the distance between nozzles in the printhead define the native vertical resolution of the printer. The minimum distance between two spots of ink deposited on the recording medium by the same nozzle define the native horizontal resolution of the printer. In a xerographic print engine, one or more data-modulated laser light beams scan over a xerographic photoreceptor in accordance with a predetermined raster scanning pattern. The minimum distance between two spots consecutively formed by the same laser light beam on the photoreceptor defines the native horizontal resolution of the printer. The distance between two scans on the photoreceptor by the same laser light beam define the native vertical resolution of the printer. More generally, any type of printer has a native horizontal resolution and a native vertical resolution.
Image scanning has assumed increased importance for applications such as desktop publishing, image processing and World Wide Web publication. Currently, image scanning is generally done using either high-end drum scanners or low-end flatbed scanners.
Images are represented in a wide variety of manners using various techniques. Illustratively, an image may be represented in the form of a grayscale image, i.e., a continuous tone image. In such a representation, multiple grayscale values are used to create the varying portions of the image. Such a grayscale image may be composed of pixels that possess values in the range of 0-255, for example, resulting in the image possessing 256 possible grayscale values.
Further, images may be represented in binary form. Illustratively, a continuous tone image may be converted or xe2x80x9chalftonedxe2x80x9d and represented in a binary form. In a binary form, an image is represented by creating halftone cells or dots. Each cell represents a grayscale value within an area of pixels. The pixels in the binary image may be either on or off, i.e., black or white, respectively. By turning the pixels in an area of the binary image on or off, a grayscale value may be simulated. As a result, the binary image can replicate the entire grayscale image without using continuous tones.
In particular, the binary image may be a high addressability binary image. A high addressability binary image is an image created by a device such that the spatial addressability of the writing spot is finer than the size of the writing spot. High addressability also often refers to an addressability resolution in a first direction is finer than the spatial addressability resolution in a second direction perpendicular to the first direction, for example.
Input scanners typically acquire image information possessing 256 levels of gray to represent a spot or pixel in the scanned image. In general, image output devices such as printers, for example, are only capable of creating spots within an area with a limited predetermined spatial resolution, based on the native horizontal and vertical resolutions. In contrast to the gray-scale resolution of a scanner, output devices generally use only two gray-scale levels, or some other relatively small number of levels, to reproduce image information. As a result, output devices commonly contend with excess gray-scale resolution information by quantizing the image data through halftoning techniques to represent the image as a halftone, i.e., a binary image possessing two grayscale levels.
When either one or both of the horizontal and vertical scanning resolutions is higher than the corresponding native resolution(s) of the target printer, the scanning process is less efficient because a higher speed and a smaller number of pixels could have achieved the same printing result.
Moreover, when a ratio between one of the horizontal and vertical resolutions of a scanner and the corresponding resolution of a printer is not a power of 2, moirxc3xa8 patterns can occur, which are detrimental to the accurate rendering of the image. Moire patterns are xe2x80x9cbeatingxe2x80x9d, i.e., periodically mismatching, patterns of interference that degrade resulting rendered images.
Accordingly, there is a need in the art for a scanning method and device outputting an image to a print engine which allows for the printing characteristics of individual objects that are appropriate to the print engine, for example, with a vertical and horizontal resolutions that match the corresponding resolutions of a target printer, while simultaneously avoiding using large memory zones for each individual object.
According to one exemplary embodiment of this invention, an image scaling method utilizes the controllable scanner resolution with its segmentation and scaling intelligence to deliver a digital image scaled to a printer""s native resolution.
These and other features and advantages of this invention are described in or are apparent from the following detailed description of the system and methods according to this invention.